Footnotes

• Contributors MI: study conception and design, data acquisition, analysis and interpretation of data, drafting of the manuscript, critical revision of the manuscript for important intellectual content. TLP: analysis and interpretation of data, drafting the manuscript. AB: statistical analysis. SG: study conception and design, data acquisition, analysis and interpretation of data, drafting of the manuscript. VV: analysis and interpretation of data, drafting the manuscript. XG: study conception and design, data acquisition, analysis and interpretation of data, drafting of the manuscript.

• Funding The NIHR Biomedical Research Centre supports MI at the University Hospitals Birmingham NHS Foundation Trust and the University of Birmingham.

• Disclaimer The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health.

• Competing interests None declared.

• Provenance and peer review Not commissioned; internally peer reviewed.